C-arm fluoroscopy machines are often used in hospital emergency rooms and trauma centers. These machines have an arm which supports an x-ray source spaced apart from an x-ray detector. The arm can be manipulated to place the x-ray source on one side of a patient and the x-ray detector on the other side of the patient. A series of joints permits the arm to be moved to a pose which will provide a desired x-ray image. A monitor displays the x-ray image in real time.
C-arm fluoroscopy machines may, for example, be used to image the locations at which pins or screws will be inserted to hold broken bones in place.
One issue with the use of C-arm fluoroscopy machines is limiting the amount of x-rays to which physicians and other medical personnel are exposed. In many procedures a physician's hands will be in the field irradiated by x-rays. Although modern x-ray machines can acquire acceptable images with a lower dose than was formerly possible there is a limit to the dose reduction that can be achieved by this route.
Another approach to reducing x-ray exposure to medical personnel is reducing the amount of time required to obtain desired images. Providing a mechanism to track the position of an x-ray source and detector can help to reduce the time taken to obtain desired images. A tracking system may also facilitate a range of useful functionalities that are based on known spatial positions of radiographs relative to one another and to a patient.
Optical localizers have been proposed for tracking the position of the arms of C-arm fluoroscopy machines. Such localizers use cameras to track the positions of targets mounted on the C-arm. Optical trackers have a number of deficiencies. For example, the camera requires an unobstructed line of sight to the targets. This constrains the use of valuable operating room space. This problem is made worse because a C-arm is relatively large and must be able to be moved through a large range of motion. Thus maintaining an unobstructed line of sight between camera and targets places serious constraints on the positioning of other operating room equipment and operating room personnel. In addition, optical localizers can have high costs.
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There remains a need for practical and cost-effective ways to accurately track the positions of imaging devices such as C-arm x-ray fluoroscopy machines.